The field of the present invention is air driven reciprocating devices.
Pumps having double diaphragms driven by compressed air directed through an actuator valve are well known. Reference is made to U.S. Pat. Nos. 5,213,485; 5,169,296; and 4,247,264; and to U.S. Pat. Nos. Des. 294,946; 294,947; and 275,858. Actuator valves using a feedback control system are disclosed in U.S. Pat. Nos. 4,242,941 and 4,549,467. The disclosures of the foregoing patents are incorporated herein by reference.
Common to the aforementioned patents on air driven diaphragm pumps is the disclosure of two opposed pumping cavities. The pumping cavities each include a pump chamber housing, an air chamber housing and a diaphragm extending fully across the pumping cavity defined by these two housings. Each pump chamber housing includes an inlet check valve and an outlet check valve. A common shaft typically extends into each air chamber housing to attach to the diaphragms therein.
An actuator valve receives a supply of pressurized air and operates through a feedback control system to alternately pressurize and vent the air chamber side of each pumping cavity through a control valve piston. Feedback to the control valve piston has been provided by the position of the shaft attached to the diaphragms which includes one or more passages to alternately vent the ends of the valve cylinder within which the control valve piston reciprocates. By selectively venting one end or the other of the cylinder, the energy stored in the form of compressed air at the unvented end of the cylinder acts to drive the piston to the alternate end of its stroke. The pressure builds up at both ends of the control valve piston between strokes. Pressurized air is allowed to pass longitudinally along the piston within the cylinder to the ends of the piston. Consequently, a clearance has typically been provided between the control valve piston and the cylinder.
Under proper conditions, the shifting energy is more than sufficient to insure a complete piston stroke. However, under adverse conditions, the damping or resistance to movement of the piston may so increase relative to the pressure available that the system may require all available potential energy for shifting of the piston. Under such marginal conditions, all possible energy is advantageously applied to insure operation of the actuator valve. One mechanism for providing additional energy for shifting is presently included in the devices of the aforementioned patents. Additional compressed air is supplied through passageways to the expanding chamber at one end of the control valve piston. The air is gated into the passageways by the location of the piston. Control of that energy in the control valve assembly itself is also important. Reference is made to U.S. patent application Ser. No. 09/063,253, the disclosure of which is incorporated herein by reference.
Air driven systems, using the expansion of compressed gasses to convert potential energy into work, can experience problems of icing when there is moisture in the compressed gas. As the gas expands, it cools and is unable to retain as much moisture. The moisture condensing from the cooled gas can collect in the passageways and ultimately form ice. This can result in less efficient operation and stalling. One solution is to be found in U.S. Pat. No. 5,607,290, the disclosure of which is incorporated herein by reference.
The control of expansion of the compressed gasses can be aided by a diffuser outlet from the valve for self purging. The diffuser allows a distribution of expanding gases from a constrained area with a diverging surface making ice formation difficult. One such system is disclosed in U.S. Pat. No. 5,957,670, the disclosure of which is incorporated herein by reference.
Relief valves controlling control valve assemblies are disclosed in U.S. patent application Ser. No. 08/842,377, the disclosure of which is incorporated herein by reference. The valve, independently configured, provides positive opening characteristics through the accumulation of energy before actuation.